Recent questions tagged difficult

An electrical technician requires a capacitance of $2 \mu F$ in a circuit across a potential difference of $1\; kV$. A large number of $1\; \mu F$ capacitors are available to him each of which can withstand a potential difference of not more than $400\; V$. Suggest a possible arrangement that requires the minimum number of capacitors.

asked Jan 3, 2017 by meena.p

1 answer

A spherical capacitor consists of two concentric spherical conductors, where outer and inner radii are $r_1$ and $r_2$ respectively as shown in the figure.The capacitance of the spherical capacitor is

asked Jan 3, 2017 by meena.p

1 answer

In a hydrogen atom, the electron and proton are bound at a distance of about $0.53 \dot{A}$: What is the minimum work required to free the electron, given that its kinetic energy in the orbit is half the magnitude of potential energy obtained ?

asked Jan 2, 2017 by meena.p

1 answer

A cylindrical capacitor has two co-axial cylinders of length $15\; cm$ and radii $1.5\; cm$ and $1.4\; cm$. The outer cylinder is earthed and the inner cylinder is given a charge of $3.5\; \mu C$. Determine the capacitance of the system and the potential of the inner cylinder. Neglect end effects (i.e., bending of field lines at the ends).

asked Jan 2, 2017 by meena.p

1 answer

A $600 \;pF$ capacitor is charged by a $200\; V$ supply. It is then disconnected from the supply and is connected to another uncharged $600 \;pF$ capacitor. How much electrostatic energy is lost in the process?

asked Jan 2, 2017 by meena.p

1 answer

If each diode in the figure has a forward bias resistance of $25\;\Omega$ and infinite resistance in reverse bias , What will be the values of the current $I_1, I_2, I_3$ and $I_4$ ?

asked Jan 2, 2017 by meena.p

1 answer

A zener of power rating 1W is to be used as a voltage regulator . If Zener has a breakdown of $5V$ and it has to regulate the voltage which fluctuated between $3\;V$ and $7\;V$, What should be the value of $R_s$ for Safe operation .

asked Jan 2, 2017 by meena.p

1 answer

ODBAC is a fixed rectangular conductor of negligible resistance (co is not connected) and OP is a conductor which rotates clockwise with an angular velocity $w$ as shown in the fig. The entire system is in a uniform magnetic field B whose direction is along the normal to the surface of the rectangular conductor ABDC. The conductor OP is in electric contact with ABDC. The rotating conductor has resistance of X per unit length. Find the current in the rotating conductor as it rotates by $180^{\circ}$

asked Jan 1, 2017 by priyanka.c

1 answer

A conducting wire XY of mass $m$ and negligible resistance slides smoothly on two parallel conducting wire as shown in the fig. The closed circuit has a resistance R due to AC. AB and CD are perfect conductors. There is a magnetic field $B = B (+) \hat {k}$ . Is there a decrease in kinetic energy of XY equalling the heat lost in R ?

asked Jan 1, 2017 by priyanka.c

1 answer

A conducting wire XY of mass $m$ and negligible resistance slides smoothly on two parallel conducting wire as shown in the fig. The closed circuit has a resistance R due to AC. AB and CD are perfect conductors. There is a magnetic field $B = B (+) \hat {k}$ If B is independent of time, obtain $V (t)$ assuming $V(0) = u_0$

asked Jan 1, 2017 by priyanka.c

1 answer

A magnetic field $B =B_o \sin(wt) \hat{k}$ covers a large region where a wire AB slides smoothly over two parallel conductors separated by a distance d, as shown in the fig. The wire are in the x-y plane. The wire AB (of length d) has resistance R and the parallel wires have negligible resistance. It AB is moving velocity $v$, what is the force needed to keep the wire at constant velocity ?

asked Jan 1, 2017 by priyanka.c

1 answer

A conducting wire XY of mass $m$ and negligible resistance slides smoothly on two parallel conducting wire as shown in the fig. The closed circuit has a resistance R due to AC. AB and CD are perfect conductors. There is a magnetic field $B = B (+) \hat {k}$ write down the equation for the acceleration of the wire XY.

asked Jan 1, 2017 by priyanka.c

1 answer

Consider a metal ring kept (supported by a cardboard) on top of a fixed solenoid carrying a current $I$ as shown in the fig : The centre of the ring coincides with the axis of the solenoid. If the current in the solenoid is switched off, What happens to the ring ?

asked Jan 1, 2017 by priyanka.c

1 answer

Consider a metal ring kept on top of a fixed solenoid (say on a cardboard) as shown in the figure. The centre of the ring coincides with the axis of the solenoid. If the current is suddenly switched on, the metal ring jumps up. Explain.

asked Dec 31, 2016 by priyanka.c

1 answer

Obtain an expression for the mutual inductance between a long straight wire and a square of side a as shown in the figure .

asked Dec 31, 2016 by priyanka.c

1 answer

An air-cored solenoid with length 30cm, area of cross section $25 cm^2$ and number of turns 500, carries a current of 2.5A. The current is suddenly switched off in a brief time of $10^{-3}S.$ How much is the average back emf induced across the ends of the open switch in the circuit ? Ignore the variation in magnetic field near the ends of the solenoid ?

asked Dec 31, 2016 by priyanka.c

1 answer

A square loop of side 12cm with its sides parallel to X and Y axes is moved with a velocity of 8 cm/s in the positive X-direction in an environment containing a magnetic field in the positive Z-direction. The field is neither uniform in space nor constant in time. It has a gradient of $10^{-3}$T/cm along the negative X-direction (that is it increases by $10^{-3}$T/cm as one moves in the negative X-direction) and it is decreasing in time at the rate of $10^{-3} $ T/S. Determine the direction and magnitude of the induced current in the loop if its resistance is $4.50 m\Omega$

asked Dec 30, 2016 by priyanka.c

1 answer